The Electronic Travel Authorization (ETA) is needed for nationals of most Temporary Resident Visa (TRV) exempt countries prior to eligibility to fly to Canada. Those subject to the TRV requirement would need to apply to a visa office for an entry visa but would not normally be eligible for travel on the basis of an ETA.
The government of Canada has introduced provisions allowing nationals of Brazil, Bulgaria, and Romania to fly to Canada on the basis of an ETA alone (i.e., without first applying for a TRV at a visa office) under the following circumstances:
1. The individual has held a Canadian visitor visa in the past 10 years, or
2. The individual currently holds a valid United States non-immigrant visa.
Such an individual flying to or transit through a Canadian airport using a valid Brazilian, Bulgarian or Romanian passport, and seeking admission for business or tourist activity of up to six months, may now apply for an ETA and fly to Canada on that basis if approved. Note that this does not mean that such an individual becomes eligible for processing of a work permit application at a port of entry, which remains reserved for those with TRV exemption.